Bad aquastat?


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Old 11-28-11, 07:52 AM
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Bad aquastat?

I have an L8148A aquastat, on our Weil-McLein (both about 28 years old). The system was drained down this summer when I had to replace a circulator pump. It is refilled, and all radiators bled. When the thermostat calls for heat now, I noticed that the pipes/radiators don't get very hot. Temp/pressure gauge on the system said it was about 18 lbs at about 120 degrees. I opened the aquastat and dialed it up from about 140 to now indicate 200. When it runs now, it reports about 140 degrees. Is it possible that the boiler could have air in it? Should I replace the aquastat? I've seen on other posts the suggestion to replace the L8148 with an L7224U1002. Does this make sense in this application? One other issue that might be relevant. I notice that the aquastat seems to make a low level hum almost constantly. The transformer? Is this normal? Sorry for lots of questions, and I know that in responding you'll likely need more info. Thanks in advance!
 
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Old 11-28-11, 09:35 AM
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With a multimeter, see if contacts on the aquastat are closing when the boiler temp is below the setpoint and there is a heat call. It sounds like they are not.
 
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Old 11-28-11, 03:10 PM
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It is refilled,
How did you actually refill the boiler? How confident are you that it is full? ( I'm guessing not very, since you are raising the questions.)

dialed it up from about 140 to now indicate 200
140 is low for a high limit setting, and 200 is probably needlessly high. I would set it at 180.

Is it possible that the boiler could have air in it?
Yes it's possible...

It's also possible that the thermometer on the boiler is defective.

replace the L8148 with an L7224U1002. Does this make sense in this application?
If the aquastat is in fact bad and a replacement is needed, you could use the 7224, but you could also just as easily replace with the same thing... unless you have a compelling desire to use some of the optional features of the 7224 it won't really get you 'ahead' of using another 8148. That said, you may find that the 7224 comes in a few bucks cheaper than the 8148.

Patriot Supply - L7224U1002

Patriot Supply - L8148A1017

Diagnose the problem fully before changing parts.

the aquastat seems to make a low level hum almost constantly. The transformer? Is this normal?
Yes probably the transformer. Normal? I guess it depends on how loud it actually is. If you have to strain to hear it, yes, I would call that normal. If it's so loud that you can hear it upstairs with the TV on, no, that's not normal. I would say most likely it's a 'non-issue' based on your description.
 
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Old 11-28-11, 04:21 PM
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Originally Posted by NJ Trooper
How did you actually refill the boiler? How confident are you that it is full? ( I'm guessing not very, since you are raising the questions.)
Before filling the boiler I checked the expansion tank (bladder type) which was low, so I attached a bike pump to it and brought it to recommended pressure. I filled the boiler by opening the valve on the supply pipe and letting it run until no more sound of water entering the system. Then bled radiators from the top down. After doing all this, the system was cleaned and tuned for the season by a tech from the oil company, but he did not run the system long enough to see the final temperature of the water.
I'm reasonably confident that it is full, but not completely (confident), as I read on another thread about the probe well possibly not being immersed in water. But, would I be likely to have successfully bled the radiators on first and second floor with water still in the boiler? Is there a way to bleed the boiler itself?


140 is low for a high limit setting, and 200 is probably needlessly high. I would set it at 180.
I pushed it up to see if somehow calibration was off. Raising the limit did have the effect of bringing up the water temperature, but only from 120 or so to 140.


Yes it's possible...

It's also possible that the thermometer on the boiler is defective.
I don't think the thermometer is that far off, as I can easily grasp the pipes which I could not do when it was operating well in the past.


Yes probably the transformer. Normal? I guess it depends on how loud it actually is. If you have to strain to hear it, yes, I would call that normal. If it's so loud that you can hear it upstairs with the TV on, no, that's not normal. I would say most likely it's a 'non-issue' based on your description.
No, not loud outside the basement. Just loud enough to detect. I can stop the noise by holding the aquastat housing, which seems to stop any vibration.

Gilmorrie, I tried to test with the multimeter, a tool with which I am not terribly adept. If I was using the correct contacts (outside of the adjuster dial), and if I was using the correct scale on the multimeter, the reading was .8 when the thermostat was not calling for heat, and .4 when it was.
 

Last edited by NJT; 11-28-11 at 06:42 PM. Reason: fixed quotes
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Old 11-29-11, 03:17 AM
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follow-up thought to question of boiler being full or not

I spent a lot of time in bed thinking about this last night. If the boiler somehow had enough air in it to have the probe's well not immersed, wouldn't my problem be the flame running too long and water overheating, since the aquastat would not know that it was reaching high limit temp? Just a thought.
 
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Old 11-29-11, 06:44 AM
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To bleed the boiler lift the leaver on the 30 psi. safety valve.The tune up tech. should have done this to insure that it works as part of his safety checks.
 
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Old 11-29-11, 06:57 AM
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Thanks Saves. I'll do this later today. I've been reluctant to do it as last time I used it, a few years ago, I had a hard time getting it to stop dribbling completely. I suppose I should just go ahead and replace it. Maybe this time. It is warm out now, so a good time to try it.
 
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Old 11-29-11, 11:42 AM
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I just bled the system through the pressure relief valve and there was no appreciable air in it. Is this sounding more like the aquastat?
 
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Old 11-29-11, 12:46 PM
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No not to me, if the aqua stat is humming that should mean that there is a call for heat and the burner is on until the boiler water reaches high temperature setting.
 
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Old 11-29-11, 01:13 PM
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Saves, the hum is pretty constant regardless of whether or not there's a call for heat. If I touch the edge of the transformer I can make the hum stop.
 
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Old 11-29-11, 02:05 PM
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If you take one wire off terminal TT dose it still hum?
 
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Old 11-29-11, 02:12 PM
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I'll try when I get home tonight and let you know.
 
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Old 11-29-11, 02:49 PM
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If the boiler somehow had enough air in it to have the probe's well not immersed, wouldn't my problem be the flame running too long and water overheating, since the aquastat would not know that it was reaching high limit temp?
Yes, I agree with that.

reluctant to do it as last time I used it, a few years ago, I had a hard time getting it to stop dribbling completely. I suppose I should just go ahead and replace it.
Which is the reason I didn't suggest it... let's not fix something so much that we break it! One problem at a time... stay focused!

If the relief valve is over 5 years old, just replace it... next time...

One 'trick' that sometimes works for a dribbling valve, and sometimes not... lift the handle all the way up and release and let it 'snap' shut.

If I touch the edge of the transformer I can make the hum stop.
This is simply the transformer vibrating. New transformers are generally quiet, as they age the laminations and windings loosen and they hum a bit. NOTHING TO WASTE TIME DIAGNOSING!

Is this sounding more like the aquastat?
Yes it is. If you are confident that the temp gauge is not lying to you, and with the a'stat set at 200 it still cuts the burner off at 140, then it's probably safe to call the a'stat to the carpet.

Are you sure that there are no other high limit controls, etc, wired in series with the limit switch?
 
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Old 11-29-11, 05:10 PM
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NJ Trooper, Thanks for your responses. I'm not real experienced with this arena (as you can tell), but you're confirming my logic. It is a pretty simple looking installation and I don't see any other things that look like they could be high limit controls. I think I'll bite the bullet and order a new aquastat and go ahead and swap it out. I'll let you know how this works.
 
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Old 12-02-11, 07:54 AM
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I just finished installing and testing a new aquastat and all seems to be right with the world, well, almost all. The system runs fine and the water now got up to about 175 degrees with the adjuster set at 180. the thermostat stopped calling for heat before it got all the way to 180, as it is not too cold outside. Thanks very much for your advice and giving me the confidence to go ahead with this. By the way, I ordered the part from PexUniverse.com and they got it to me in just over 24 hours, on the cheapest shipping option. Great price and service - I'd recommend them.
One question: A relatively new (1 year old) circulator pump motor gets pretty hot during extended operation. To the point that I can't leave my hand on the motor housing. Is this normal? We used to run a B and G "little red pump" and I don't remember it getting nearly that hot.
Thanks again!!
 
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Old 12-02-11, 09:34 AM
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Originally Posted by Baltimore Lou
One question: A relatively new (1 year old) circulator pump motor gets pretty hot during extended operation. To the point that I can't leave my hand on the motor housing. Is this normal? We used to run a B and G "little red pump" and I don't remember it getting nearly that hot.
Your old B&G pump was a three-piece dry-rotor pump. What is the make and model of your new pump? If it's a wet-rotor pump, and running the boiler temp at 180 deg, and you're pumping away from the boiler, it will run at 180 deg, plus.
 
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Old 12-02-11, 03:55 PM
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gilmorrie,
The new pump is a Taco 007. I did not even consider that this was the water temp making the pump hot. Perhaps, but what I think I'm feeling is the motor section of the pump rather than the rotor section. It was running hot even before the new aquastat raised the water temp.
 
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Old 12-02-11, 04:02 PM
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The Taco 007 is a canned motor pump. The rotor is immersed in the hot water being pumped, unlike your old B&G pump. The motor and the pump are all one "section," not separate. It has only one moving part - the rotor (cartridge), which includes the impeller and the motor. You could buy another cartridge - if, as I suspect, it makes no difference, you'll have a spare. Or, just stop worrying.
 
 

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